Poly(ester amide)s (PEA)s are useful as polymeric carriers of bioactive substances when coated on implantable medical devices such as stents to reduce restenosis and other problems associated with the treatment of atherosclerosis (see, e.g., U.S. Pat. No. 6,503,538, B1).
PEAs can be made by condensation polymerization of a diamino compound with a diester dicarboxylic acid (Scheme I). In Scheme I, the dicarboxylic acids are converted to an active di-p-nitrophenyl derivative to facilitate the polymerization.
When the dicarboxylic acid and the diamino subunits are used stoichiometrically, the PEA formed has one terminal carboxylic acid group and one terminal amino group. When the dicarboxylic acid and the diamino subunits are not used in a 1:1 ratio, the PEA formed can have excess terminal carboxylic acid groups if more of the dicarboxylic acid subunit is used or excess terminal amino groups if more of the diamino subunit is used.

Reactive end groups in PEAs can be problematic. First, since active amino and active carboxyl end groups are present, polymerization can continue. Second, if the PEA formed is combined with a drug that possesses an functional group capable of reacting with a carboxyl (activated or unactivated) or amino group, it is possible that the drug will react and covalently attach to the PEA, essentially rendering the drug unavailable for therapeutic use.
What is needed are PEAs in which the end groups are rendered inactive so as to avoid the above problem and any other than might arise because of the presence of the active terminal functional groups. The present invention provide such PEAs and methods for preparing them.